1. Field of the Invention
The present invention relates to an electric connector, and more particularly to an electric connector of plug-and-socket type which permits the insertion of the male plug into the female socket with a reduced insertion force.
2. Description of the Prior Art
As is well known, electric connectors of plug-and-socket type have been widely used. The male plug has pin terminals each having parallel opposite sides and converging slant surfaces whereas the female socket has contacts each having contact pieces and being adapted to accomodate the corresponding pin terminal, keeping the parallel opposite sides and converging slant surfaces of the pin terminal in resiliennt contact with the contact pieces of the contact.
FIG. 6 shows such a conventional electric connector of plug-and-socket type. As shown, the tapering end of a pin terminal 1' has opposite slant surfaces 2' and 3' symmetrical with respect to the center axis C' of the pin terminal rod. Likewise, a pair of contact pieces are symmetrical with respect to the center axis C' of the contact. FIG. 5 shows how the insertions force (ordinate) varies with the insertion depth (abscissa).
As seen from this graph, as the pin terminal proceeds towards the final contact position with the tangential angle increasing, the insertion force increases until it has reached its peak value F.sub.1. This value is generally called "insertion force". When the parallel opposite sides of the pin terminal reach the contact pieces, the tangential angle is trimmed exactly into desired curved surface by removing stretched portions from the punched piece or by reshaping somewhat deformed portions of the punched piece. This work is difficult, and therefore pin terminal each having more or less different curvatures on its opposite sides are likely to result. Thus, the insertion force cannot reach its peak value on each side at a controlled time. Stated otherwise, the precise shaping of curved surfaces on the opposite sides of the pin terminal requires the corresponding precision in punching dies used and in subsequent trimming work.